Many forms of balers are well known today. The most commonly used field baler of today forms a rectangular bale by picking up crop material by means of a crop pickup, transferring the crop material laterally by means of packer fingers to the forward end of a bale chamber, and then compressing the crop material into a bale within the bale chamber by means of a plunger. The baler also includes a bale tying mechanism including a needle and knotter, the needle and knotter being driven through a single revolution clutch from a constantly running member whose rotational movement is coordinated with the movement of the plunger through a mechanical drive. The baler further includes a metering mechanism which measures the length of the bale being formed and initiates operation of the tying mechanism through a single revolution clutch of the dog type, the dog engaging a cam on the constantly running member whose rotation is coordinated with the movement of the plunger by mechanical drive means in the form of chains or the like.
While this form of baler has achieved wide spread commercial success in the past, high peak loads are encountered during the operation of the baler which require relatively heavy drive train components. Since the prior art balers are customarily drawn by a tractor it is common practice to drive the baler from the tractor power take-off. It has been proposed in a related patent application to feed the crop material into the bale case on the baler by means of a pair of reciprocated rollers which are moved back and forth across the inlet end of the bale chamber. This form of construction substantially simplifies the drive of a baler since high peak torques are minimized, thus permitting the utilization of the hydraulic power readily available on the propelling tractor. Since hydraulic power may be utilized to operate the feeding means, it is also desirable to utilize hydraulic power for the operation of the bale tying mechanism, thus eliminating mechanical drive line components between the tractor and the baler. However, it should be appreciated that if the operation of the feeding mechanism and the tying mechanism are not timed with respect to each other, that the baler will not perform in a satisfactory manner. In addition, it is not possible to achieve coordination of two hydraulic motors which are not mechanically interconnected with each other through the operation of a fluid circuit per se.